The present invention relates to an apparatus for reproducing data from a disk such as a CD (compact disk), an MD (mini disk) and a DVD (digital versatile disk), and a reproduction control circuit.
At present, a digital recording/reproduction system in which an audio signal is converted to a digital signal by the PCM (pulse code modulation) technique and the digital signal is recorded on a recording medium such as a disk and a magnetic tape and reproduced therefrom, is known as one for achieving high-density and high-fidelity recording/reproduction in the field of acoustic equipment. In particular, a CD in which a pit string corresponding to digital data is formed on a 12-cm-diameter disk and read out optically, is the most popular. The CD is rotated by causing an optical pickup including a semiconductor laser and a photoelectric transducer to linearly track the disk from its inner radius to its outer radius and by rotating the disk at CLV (constant linear velocity) to read data out of the disk. In addition to the CD, a CD-ROM and a DVD are known as a data reproduction apparatus.
The data reproduction apparatus such as a CD and an MD has a function of setting a data readout velocity higher than a given reproduction velocity, storing readout data in a semiconductor memory, and reading the data out of the memory at the reproduction velocity, for the following two reasons.
(1) In a portable CD player and a portable MD player, the resistance to vibrate at the time of data reproduction is increased as follows (audio data can be reproduced continuously even though any vibration is applied to the player from outside). Data is stored in advance in a semiconductor memory. If readout of data from a disk is interrupted due to vibration, the interruption is compensated for the data stored in the memory, and the readout is restarted before all the data is read out of the memory. The data can thus be reproduced without interruption.
(2) In a peripheral storage apparatus of information equipment (host) such as a CD-ROM drive, data can be transferred to the host through an I/F (interface) at high velocity by request therefrom since a signal read out of a disk is stored in a semiconductor memory.
Even in the above CD-ROM drive, an audio signal needs to be reproduced from a CD-DA (CD-digital audio) disk, whereas digital data is read from a CD-ROM disk at velocity which is much higher than a given reproduction velocity of the CD-DA disk. When CD-ROM data and CD-DA data are recorded on a single disk and both are frequently reproduced therefrom, the former data is reproduced at high velocity and the latter data is done at given velocity. Therefore, the abrupt acceleration and deceleration of rotation of the disk have to be repeated, which increases the power consumption of a rotation control system. Moreover, it becomes more difficult to design a control circuit for controlling both CD-ROM and CD-DA sections by one motor and one pickup element.
For the purpose of reducing power consumption and simplifying the configuration of the control circuit, the above problems can be resolved as follows. Even when CD-DA data is reproduced, data is read out of a high-velocity disk and temporarily stored in a semiconductor memory. The data is thus read from the memory at the given velocity.
The system configuration of a reproduction apparatus having the above function (1), such as a portable CD player and a portable MD player, is illustrated in FIG. 13.
In the apparatus in FIG. 13, a disk 1 is rotated by a disk rotation control circuit 2, a disk motor driving circuit 3 and a disk motor 4 at CLV which is higher than predetermined velocity. A pickup element 5 linearly tracks the rotating disk 1 from its inner radius to its outer radius to read data out of the disk 1. The data read by the pickup element 5 is amplified by a head amplifier 6 and converted to a wide-band signal (RF signal). The RF signal is then converted to binary data of only two high and low levels by a binarization circuit 7. The binary data is supplied to a PLL (phase locked loop) circuit 8 and a signal processing circuit 9. In the circuit 9, first, a synchronization signal separation circuit 10 separates a synchronization signal from the RF signal, and then sends the synchronization signal to the disk rotation control circuit 2 and sends reproduction data excluding the synchronization signal to a demodulation circuit 11. The reproduction data is demodulated by the circuit 11 and error-corrected by an error-correction circuit 12. The error-corrected data is written to a memory 14 directly or through a compression circuit 13 in response to a clock signal generated by the PLL circuit 8, which is synchronized with an RF signal. The MD does not necessitate the compression circuit 13 because compressed data is already recorded thereon. In the CD, data compressed by the compression circuit 13 is written to the memory 14 to reduce the capacity of the memory 14.
Even in the CD's case, data may be written to the memory 14 directly without being compressed. The data is read out of the memory 14 at predetermined reproduction velocity in response to a readout clock signal generated from a crystal oscillator 15 and then supplied to an output processing circuit 17 as it is or through an extension circuit 16. The MD requires the extension circuit 16 because compressed data is already recorded thereon. The CD needs the circuit 16 only when data is compressed to reduce the capacity of the memory 14, and not when data is written to the memory 14 directly without being compressed. The data supplied to the output processing circuit 17 is output as digital data, converted to an analog signal using a D/A converter 18, or converted to a digital output signal using a digital audio I/F 19.
The sub-code information separated in the demodulation circuit 11 is transmitted to a sub-code processing circuit 20 and its address information is demodulated. The rotation control circuit 2 generates a control signal having a CLV from the synchronization signal and sends it to the disk motor driving circuit 3 to control the disk motor 4 at CLV.
A system controller (microprocessor) 21 monitors an amount of data in the memory 14 and address information from the sub-code processing circuit 20 and controls writing of data to the memory 14 to prevent the memory 14 from overflowing. The pickup element 5 is thus controlled. If a readout operation of the disk 1 is interrupted due to vibrations from outside, the system controller 21 causes the readout operation to be restarted.
If, in the above reproduction apparatus, data is read out of the disk at velocity which is higher than predetermined reproduction velocity, i.e., at velocity twice as high as the reproduction velocity, the velocity at which data is written to the memory becomes twice as high as the velocity at which data is read therefrom and thus data can always be stored in the memory. When the pickup element is affected by vibrations from outside to interrupt a read operation of the disk, if data is read out of the memory, the output of reproduction signals is not interrupted but the pickup element is controlled and the read and write operations can be restarted. The reproduction signals can thus be output without interruption to improve the resistance of the apparatus to vibrate.
The system configuration of a reproduction apparatus having the above function (2), such as a CD-ROM drive, is illustrated in FIG. 14.
In the reproduction apparatus in FIG. 14, a disk 1 is rotated by a rotation control circuit 2, a disk motor driving circuit 3 and a disk motor 4 at CLV or CAV (constant angular velocity) which is higher than predetermined velocity. The disk motor driving circuit 3 or disk motor 4 sends an FG signal indicative of angular velocity information to the rotation control circuit 2.
A pickup element 5 linearly tracks the rotating disk 1 from its inner radius to its outer radius to read data out of the disk 1. The data read by the pickup element 5 is amplified by a head amplifier 6 and converted to a wide-band signal (RF signal). The RF signal is then converted to binary data of only two high and low levels by a binarization circuit 7. The binary data is supplied to a PLL circuit 8 and a signal processing circuit 9. In the circuit 9, first, a synchronization signal separation circuit 10 separates a synchronization signal from the RF signal, and then sends the synchronization signal to the rotation control circuit 2 and sends reproduction data excluding the synchronization signal to a demodulation circuit 11. The reproduction data is demodulated by the circuit 11 and error-corrected by an error-correction circuit 12. The error-corrected data is written to a memory 14 directly or through a CD-ROM decoding circuit 22 in response to a clock signal generated by the PLL circuit 8, which is synchronized with an RF signal. A CD-ROM disk necessitates the CD-ROM decoding circuit 22, and not a CD-DA disk. The data is read out of the memory 14 at given reproduction velocity in response to a clock signal generated by a crystal oscillator 15 and then supplied to an output processing circuit 17.
In the CD-ROM disk, a signal is output through an I/F circuit 23. In the CD-DA disk, a signal is converted to an analog signal by a D/A converter 18 and then output from the circuit 17 or it is converted to a digital signal by a digital audio I/F 19 and then output therefrom.
In the signal processing circuit 9, the sub-code information is transmitted to a sub-code processing circuit 20 and its address information is demodulated. The rotation control circuit 2 generates a control signal having a CLV from the synchronization signal or generates a control signal having a CAV from the FG signal (angular velocity information) and sends it to the disk motor driving circuit 3 to control the disk motor 4 at CLV or CAV. A system controller (microprocessor) 21 monitors an amount of data in the memory 14 and address information from the sub-code processing circuit 20 and controls writing of data to the memory 14 to prevent the memory 14 from overflowing. The pickup element 5 is thus controlled.
Assume, in the above-described apparatus, that CD-ROM data and CD-DA data are recorded on a single disk and both are reproduced frequently therefrom. The CD-DA data as well as the CD-ROM data is read from the disk at high velocity and stored in a semiconductor memory, and then the data is read from the memory at given velocity. Since, therefore, both the CD-ROM data and CD-DA data can be reproduced without abruptly accelerating and decelerating the rotation of the disk, its power consumption is prevented from increasing. Since the rotation speeds for reading the CD-ROM data and CD-DA data are close to each other, a control circuit can easily be designed by the same motor and the same pickup element.
According to the foregoing apparatuses, the readout velocity of the disk is always set higher than predetermined reproduction velocity and thus the power consumption of a rotation control system becomes higher than that in the readout operation performed at the predetermined velocity. Since, in the CLV control, the angular velocity of the inner radius of a disk and that of the outer radius thereof differ from each other, the motor is accelerated and decelerated whenever the pickup element is moved in and out along the radius of the disk by access and controlled at CLV, with the result that the power consumption of a motor system is increased. Since portable CD and MD players are operated by batteries, high power consumption unfavorably shortens the lifetime of the batteries.
Since, furthermore, the CLV or CAV is controlled by increasing the speed of the rotation control system, a motor having high torque has to be used as the disk motor and accordingly the motor system is likely to increase in costs.
Since, in the CLV control, a synchronization signal is detected to control the motor at CLV when a read operation is resumed after its interruption, a time is required until the rotation control system is stabilized and accordingly a preparation to resume the read operation has to be made at an earlier time and power consumption therefor is increased. In the CAV control, the rotation can always be stabilized by the FG signal; however, an FG signal generation means for generating angular velocity information is needed to control a disk on which data is recorded at CLV, such as a CD, and thus the motor system is likely to increase in costs.